Comparative DFT study of the effectiveness of p-phenylenediamine antioxidants through their coordination ability towards the late 1st row transition metals

•Geometry optimization of antioxidants and of their transition metal complexes•Elimination of complexes without exclusive metal – nitrogen bonds•Interaction energy Eint evaluation•Population analysis and topological analysis of electron density•Similar trends for antiox. effectiveness vs Eint and el. density transfer Interaction energies, metal atom charges and electron density Laplacians at bond critical points of metal – nitrogen bonds in [Aox…M]2+ complexes of a series of p-phenylenediamine antioxidants (Aox) with the late 1st row transition metals M(II) in various spin states were evaluated in order to predict the antioxidant effectiveness through their coordination ability. The complexes without exclusive metal – nitrogen bonding were excluded. All the above M2+ dications exhibit similar trends of antioxidant effectiveness relation vs. interaction energies and nitrogen-to-metal electron density transfer. The only problem is in their ability of metal – nitrogen bonding because they are strongly attracted by neighboring aromatic rings. Only copper atoms are bonded exclusively to nitrogens in all the systems under study.